<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>

.box{
	width: 100px;
	height: 100px;
	background-color:pink;
}

	</style>
</head>
<body>
	<input type="button" value="按钮">
	<div class="box"></div>
</body>
<script src="../jquery-1.12.4.js"></script>
<script>

$("input").on("click",function(){
	alert(1)
	$(".box").css("background-color","rgba(0,0,0,.5)");
})

</script>
</html>